The present invention relates to a configuration and method for water-proofing a wire harness passing through a grommet installed in a panel through hole of an automobile.
In the case where a wire harness passes through a panel which divides an engine compartment and the interior of an automobile, a grommet made from rubber or elastomer is installed in a through hole passing through the panel. The wire harness passes through this grommet, and water etc. is thereby prevented from entering the interior.
An outer circumference of a wide diameter member of the grommet has a panel engaging groove provided thereon. This groove engages an inner circumference edge of the panel through hole and the space between the grommet and the panel through hole is thus reliably sealed against moisture. A narrow diameter member of the grommet tightly receives the wire harness. The narrow diameter member is usually provided on the engine compartment side and prevents water etc. from entering the grommet.
However, if spaces exist between electric wires of the wire harness and between the wire harness and the grommet, water may pass from the engine side to the interior. Various measures have been used in the past to deal with this, such as filling the grommet with a sealant, etc.
The present inventor has previously provided the simple process of coating the electric wire spaces with a water-proofing material while the wire harness is on the assembly table, as described in JP-10-135657. As FIGS. 6-8 of this application show, in this method, on an assembly table 1, a jig 2 formed on a wire harness path is provided with a pair of electric wire supports 2a and 2b. A group of electric wires w comprising a wire harness W/H are singulated and pass through these electric wire supports 2a and 2b. While the electric wires w are supported in an aligned manner by the electric wire supports 2a and 2b, a viscous or non-liquid sealant 4 comprising silicone or the like is applied by a nozzle 3 or a brush to the electric wires w. Then, as shown in FIGS. 9 and 10, the outer circumference of the part coated with the sealant 4 is wrapped in a closed cell foam sheet 5 or a film so as to form a circular shape, and in this state the harness is passed through a grommet 6. Then an open end of a narrow diameter cylindrical member 6a of the grommet 6 is fixed to the sheet 5 with tape 7.
The above method has the advantage of being performed on a wire harness assembly table, on the wire harness assembly line. However, as shown in FIG. 11, in the case where a portion of the electric wires w supported in an aligned manner by the electric wire supports 2a and 2b crosses and becomes twisted, a space C occurs. The sealant 4 does not fill this space C and an uncovered portion Cxe2x80x2 will remain. Consequently, as shown in FIG. 12, even though the electric wires w are covered by the sheet 5 and are formed into a circular shape, the space C may not be filled with the sealant 4 due to the high viscosity thereof.
As shown in FIG. 13, the filled portion is next fastened along the narrow diameter cylindrical member 6a of the grommet 6 and the sealant 4 is urged into the portion Cxe2x80x2. However, the movement of the sealant 4 in a length-wise direction X of the electric wires is greater than the penetration of the sealant 4 in a cross-sectionally central direction Y of the wire harness. Consequently, if the central portion of the electric wires of the wire harness has the uncovered portion Cxe2x80x2. the sealant 4 often does not penetrate into that portion and merely passes along the length-wise direction of the electric wires. As a result, the uncovered portion Cxe2x80x2 will remain unsealed.
The present invention has been developed after taking the above problem into consideration, and aims to prevent the sealant from passing along the length-wise direction of electric wires, instead causing the sealant to penetrate in the cross-sectionally central direction of the wire harness, this invention reliably preventing portions from remaining unfilled with sealant.
According to the invention there is provided a method of sealing a wire harness in a grommet against the passage of moisture, the method comprising the steps of:
a) collating a bundle of wires;
b) coating the exterior of a predetermined length of said bundle with a viscous sealant;
c) wrapping said bundle with a sheet so as to cover said predetermined length and end portions on either side thereof;
d) tightly binding said end portions to confine said sealant and prevent escape thereof; and
e) inserting said predetermined length of said bundle into a tight fitting grommet of resilient material, such that the sealant is forced to permeate throughout said bundle.
Such a method both confines the sealant, and places it under resilient loading within the grommet. In this way permeation of the sealant throughout the bundle can be assured.
Preferably the end portions are bound with adhesive tape, which may be a contrasting colour in order to ensure correct relative location of grommet and wire harness. The harness and grommet may subsequently be bound together, for example by utilising a projection of the grommet extending along the length of the wire bundle. The grommet may include internal projections, preferably annular, to apply circumferential pressure to the wire bundle at specified locations.